Dealer brochures for prefab sheds, kit cabins, and backyard studios love the phrase "no permit required." It's true for some of them — but it's true only inside a narrow set of conditions, and we see cottage-country buyers get caught out by the gap between the marketing line and the actual rule almost every season. The building itself can be perfectly fine and still land you in a permit process you didn't plan for, simply because of how it was measured, how it was set up on the lot, or what got added to it after delivery.
Here's what the rule actually says, a real situation from our own files that shows how it plays out, and a checklist to run through before you buy.
What Ontario's Rules Actually Say
Start with the Building Code Act, 1992, which defines a "building" as any structure occupying more than 10 square metres, or a structure of 10 square metres or less if it contains plumbing. Above that 10 m² line, a structure is a building in the eyes of the Act — full stop.
The Building Code itself then carves out a specific, conditional exemption that lets some sheds go larger than that. Under Division C, Article 1.3.1.1, Sentence (6), a shed is exempt from needing a permit only if it meets all five of the following at once:
- not more than 15 m² in gross area;
- not more than one storey in building height;
- not attached to a building or any other structure;
- used only for storage purposes ancillary to a principal building on the lot; and
- no plumbing.
Miss any one of those five conditions and the exemption doesn't apply, even if the building is small. That's the part dealer marketing tends to flatten into a single number. A 15 m² shed with a loft used as sleeping space, or a 12 m² shed with a deck built onto it, isn't a smaller version of an exempt shed — it's simply not exempt.
A Real File: Two "Exempt" Buildings That Weren't
During the permit review for a new cottage build, the municipality's building department flagged two existing prefab storage buildings already sitting on the lot. Both had been bought as supposedly permit-exempt sheds. Both needed their own separate permit applications. That is how it always works: an accessory building is never added to the permit for the cottage or house on the same lot. The principal building and each accessory building get their own permit, whether the main permit is still in review or already issued. So each shed went in as its own application, on its own timeline.
Here's what we learned working through it, and what any cottage-country buyer should take from it.
1. Floor area is measured to the outside of the exterior walls
The Building Code defines "gross area" as the total floor area measured between the outside surfaces of the exterior walls. One of the two buildings had been sold as a 15 m² model — right at the exemption limit. But the base unit's listed dimensions didn't account for the wall insulation and cladding added after delivery. Once that was factored in, the building measured just over 16 m² on the outside face. That's it: no deck, no plumbing, nothing else involved — the wall build-up alone pushed it past the line.
Building departments do not grant "it's close" exceptions. 15.0 m² is exempt; 15.1 m² is a building that needs a permit like any other. If you're anywhere near the threshold, measure the actual exterior footprint as built, not the model number on the brochure.
2. An attached deck or platform can take away the exemption on its own
One of the two buildings was comfortably under 15 m² on its own. It had a deck built onto the front of it. Look again at condition (c) above: the shed must not be "attached to a building or any other structure." A deck is a structure in its own right. In our experience, building departments treat an attached deck as taking away the exemption on that basis alone — not because of area, but because it fails the attachment condition outright. This is our reading of how the condition gets applied in practice, and it's worth confirming directly with your building department for your specific situation; the options, if it does apply, are to remove the deck or to permit the building. There's no partial permit for "just the deck."
The same logic applies to a shed set on a separate raised platform rather than built on grade or on its own small footings: if the platform is its own structure that the shed is attached to, it raises the same question and tends to draw closer scrutiny from the building department regardless.
3. A loft can put the storey count — and the exemption — in question
Condition (b) limits an exempt shed to one storey. The Code distinguishes a true "storey" from a "mezzanine," and a small loft used for light storage may or may not tip a building into a second storey depending on how much floor area it occupies and how it's built. This is a genuine grey area that depends on the specifics of the design, not a line you can eyeball from a brochure photo. If the kit you're considering includes a loft, don't assume it still qualifies — ask your building department to look at the actual loft design before you buy, not after.
4. Manufacturer drawings may not match the current code, or what actually got built
Prefab manufacturers typically supply engineered drawings sealed by their own engineer. Those drawings are only as good as the code edition they were sealed against, and Ontario's Building Code was substantially updated for construction starting in 2025. Drawings sealed to the previous code may need to be reviewed, and potentially re-sealed, against current requirements. On top of that, what actually gets built on site — the foundation, the anchorage, any field modifications — doesn't always match the manufacturer's drawing set exactly. Reconciling the two, including an as-built redesign of the base where needed, is real engineering work, and because the scope isn't known until someone looks at the specific building, it's often billed hourly rather than quoted as a flat fee.
5. Being exempt from a permit does not mean exempt from zoning
This is the one that trips people up most often: a shed that clears every condition in Article 1.3.1.1.(6) still has to comply with your municipality's zoning by-law. Setbacks from property lines and the shoreline, maximum lot coverage, and limits on the number or total size of accessory buildings on a lot are all zoning matters, separate from the Building Code, and they apply whether or not a building permit is required. "No permit needed" is not the same question as "allowed to go there." Zoning rules vary by municipality, so confirm the specifics with your local planning or building department before you commit to a location on the lot.
6. Make sure the building is engineered for your area's snow load
This is the issue we worry about most with prefab and kit buildings, because it has nothing to do with paperwork. Snow load is set by location, and cottage country gets a lot more of it than the places many of these buildings are designed and sold for.
The Ontario Building Code takes its ground snow loads from Supplementary Standard SB-1, which lists a 1-in-50-year ground snow load (Ss) and an associated rain load (Sr) for each location. A few examples from Table 2 of the 2024 SB-1 (values are for the named municipality; your building department will confirm the figure that applies to your exact site):
- Toronto: Ss = 0.9 kPa
- Orillia: Ss = 2.4 kPa
- Gravenhurst: Ss = 2.7 kPa
- Parry Sound: Ss = 2.8 kPa
- Huntsville: Ss = 2.9 kPa
- Bracebridge: Ss = 3.1 kPa
Each of these locations also carries a rain load of Sr = 0.4 kPa. For a small house-type roof, Part 9 of the Code turns those into a design roof load with a simple formula: S = Cb × Ss + Sr, where Cb is 0.45 for a roof no more than 4.3 m wide, and the result can never be less than 1 kPa. Run that for a typical shed-sized roof and the difference is plain:
- Toronto: 0.45 × 0.9 + 0.4 = about 0.8 kPa, so the 1.0 kPa minimum governs (roughly 21 lb/ft²).
- Parry Sound: 0.45 × 2.8 + 0.4 = about 1.66 kPa (roughly 35 lb/ft²).
- Bracebridge: 0.45 × 3.1 + 0.4 = about 1.8 kPa (roughly 37 lb/ft²).
In other words, the same small roof needs to carry roughly 65–80% more snow in Parry Sound or Muskoka than it does in Toronto, and wider roofs use a higher factor still. A building whose rafters, trusses and connections were sized for a southern Ontario or out-of-province snow load can be under-designed here even though nothing about it looks wrong on the lot.
A few practical points:
- "Engineered" is not the same as "engineered for your site." Sealed drawings should state the design snow load they were based on. Check that number against the SB-1 value for your actual municipality — not a generic “Ontario” figure. If the drawings don't state a design snow load, ask the manufacturer in writing before you buy.
- An exempt shed is exempt from the Code entirely. Article 1.3.1.1.(6) exempts qualifying sheds not only from a permit but from compliance with the Code, so nobody checks the roof for you. That makes it your job to confirm the snow-load design, not a reason to skip it.
- Once the building needs a permit, the snow load has to be shown to comply. That's often where older or out-of-area manufacturer drawings fall down and need an engineer's review.
- Watch where snow slides and drifts. A shed tucked beside or below a taller cottage roof can receive snow sliding off that roof, on top of the snow that falls on it directly. Placement matters as much as the rafter size.
Before You Buy a Prefab Building: A Short Checklist
- Get the true exterior footprint. Ask for the finished outside dimensions including any insulation, cladding, trim, and attached decks or platforms — not just the base model's listed size.
- Ask for drawings sealed to the current Ontario Building Code. If the manufacturer can't confirm this, assume you may need an engineer to review or update them.
- Confirm the building is engineered for your area’s snow load. Ask what design snow load the drawings use and compare it with the SB-1 value for your municipality — cottage-country loads are far higher than Toronto’s, and a kit designed for a milder market may be under-built for your site.
- Confirm the foundation and anchorage method works for your actual site conditions, especially on rock or uneven ground.
- Be honest about intended use. A building meant for sleeping, even occasionally, falls into a different category altogether — see our guide to bunkie permit rules for how that threshold works.
- Call the building department before you buy, not after it's delivered. A five-minute phone call describing the building, its footprint, and where you want to put it can save months of back-and-forth later.
If you're planning a new cottage or home and already have outbuildings on the lot, it's worth sorting out their permit status before or while you apply for your main permit — remembering that each one will need its own separate application — rather than finding out about them partway through, as our clients did. For general background on the overall process, see our guide to cottage building permits in Ontario.
Let's Sort It Out Before You Build
Whether you're adding a prefab structure to an existing property or planning a full cottage build from French River to Orillia, getting the permit picture right before you spend money avoids the most expensive mistakes. As a BCIN-registered design firm working across Parry Sound District, Muskoka, Haliburton, and Simcoe North, a BCIN designer can prepare your permit set and help you work through existing structures, zoning questions, and new construction. Contact BrambleRidge Home Design Group to talk through your cottage-country project.
